Due to an ever-increasing demand for wireless communication services, system developers continually strive to increase the capacities of wireless systems. This is particularly true, for example, in cellular telephone systems and wireless local area network (WLAN) systems. To increase system capacities, multiple-input multiple-output (MIMO) technologies are being developed for cellular telephone and WLAN applications.
In a MIMO system, a MIMO transmitter includes multiple transmit antennas for data transmission, and a MIMO receiver includes multiple receive antennas for data reception. When signals are simultaneously transmitted by multiple antennas that are spaced more than a coherence distance apart, the signals will each have distinct spatial signatures. The coherence distance is the minimum spatial separation of antennas for independent fading, and its value depends on the angle spread of the multi-paths arriving at or departing from an antenna array. A MIMO system may provide for increased system capacity and/or quality, compared with known technologies, by exploiting the spatial diversity between the multiple antennas within an antenna array. MIMO system developers continue to try to increase system capacities by developing MIMO processing technologies that yield acceptable system performance.